I currently run tubeless 23c Schwalbe One on Zonda wheels. I briefly tried a 25c Bontrager R3 tubeless but it lacked clearance at the top of the fork and although it would fit small stones and debris would regularly jam.

So I'm thinking if I go to a wider rim, external 23 or 25mm that the tire will sit flater and not as tall as the Zonda( 20.5 wide) and then provide more clearance.

Your thoughts......

_________________All this from an old bloke who wishes he was faster and could climb better...... enjoy the ride!

It will sit taller. If you had issues with a 25mm clincher on your Zonda, it likely won't fit at all if you put the same tire on a wider rim, up at least to the point where the sidewalls go almost straight up from the bead. On your Zonda (20.5mm) a 25mm, or 23mm for that matter, the sidewalls have to curve inwards to fit in the rim. As you widen the rim a bit, that lower curve straightens out and the whole profile (height wise) of the tire gets taller. It would only start "flattening out" once you go past the point where it has straightened out, which would be a ridiculously wide rim. Folks seem to have to think about this a bit before it sinks in, or try it, like I did, before they really grasp what was happening.

Of course if the bead seat of the rim is different that will affect things, no question. But there are standard dimensions that rim manufacturers try to adhere to and the variance is minimal. It has to be, otherwise you'd have a real mess with tires not fitting certain rims at all. But all else being equal, and only considering rim width as a variable, the same clincher will sit higher on a wider rim than a narrower rim, at least to the point where the sidewall goes straight up from the rim.

Some tires are also lower in shape than others : Veloflex Corsa 23mm is "lower" than Conti4000s2 23mm .

Just my observations.

I see what you are getting at here Stormur, but couldn't it also be that some rims ride higher up the tire sidewall than others? In other words, some rims have more material, radially, beyond where the tire bead seats, which gives the appearance of the tire sitting deeper in the rim with less sidewall showing, but the actual outer diameter of the tire is unaffected.

It is kind of like this with Stans NoTubes MTB rims, where the sidewalls are only about 3.5mm high vs. other brands using 4.5mm or even 5.5mm on some of the new hookless ones. This exposes more of the tire for more pneumatic cushion, but doesn't change out outer diameter of the tire.

That might be different on a clincher road rim though, as we know from attempts to do tubeless conversions on road clinchers that the beads and casings can stretch under high pressure, which might truly allow the non tubeless tire itself to expand to a larger diameter before being "caught" by the rim hook.

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